Hello people! My in game name is Green Guy. I love playing Vel'Koz. He's absolutely amazing at nuking people down, even from full health! So I hope you enjoy this guide, and become an even better Vel'Koz player! Well good, but not good enough to beat me! :)

9 GREATER MARK OF PENETRATION (+0.87 magic penetration)
9 GREATER SEAL OF ARMOR (+1.41 armor)
9 GREATER GLYPH OF ABILITY POWER (1.19 ability power)
And last but not least,
3 QUINTESSENCE OF ABILITY POWER (+3.85 ability power)
Using these runes, you'll be able to tank better early game due to the armor, and have much more burst potential as well with the ability power. Oh, their building magic resist? EHHH! You have magic penetration so you'll go right through their defenses, and they won't know what hit them!

For masteries, I usually go with twenty-one, nine, zero. For the offense tree, I usually take cooldown reduction, and ap increases. In the defense tree, I take extra health, because you can always get through their armor.

Pros

He has good poke
He has full skillshot kit
He does massive burst damage with the right combo
He has pretty good range

Cons

He's very slow
He has full skillshot kit
He's fragile
He has to stay in the back in team fights

How to negate the cons
In order to negate these cons, there are a few things that you're gonna have to do. For the first con, which is his super slow speed, I usually go with Boots of Swiftness, but if you don't want to use those, at least get the Alacrity buff on your boots. The second one, all you can do is just practice using skillshots, especially his, cause some of his abilities are pretty unique. The third con is kinda hard to negate, you really just have to build some health with items such as Rylai's Crystal Scepter or Rod of Ages. The final con is impossible to negate, and if you try to, you'll surely die. Vel cannot handle the full focus of the enemy team, and if you go in to far, then you'll get focused because he's a new, and upredictable champion as of now.

Doran's Ring is a great starter item for any spellcaster, and ti also allows you to buy two potions in the beginning.

Fiendish Codex gives some nice cooldown reduction and also some ability power, which is very useful early game. It also builds into Athene's Unholy Grail which we'll be using later in the game.

Boots of Swiftness are amazing on Vel'Koz. One of his obvious major problems is his low speed. Although you could always just get alacrity on your boots, these just make you super fast. Of course Sorcerer's Shoes are good as well.

Rabadon's Deathcap grants massive ability power. Not only giving you plus one-hundred twenty to begin with, it also increases your ability power by thirty percent! Being an ap burster, you're gonna need all of the ap that you can get, and this is great for it.

Zhonya's Hourglass not only gives one-hundred twenty ap, but it also give you fifty armor. And I know that that's not much armor, but it can still make the difference when up against the enemies adc.

Void Staff is essential for any ap caster because it makes your magic damage ignore thirty-five percent of the enemies magic resist, which applies before magic penetration. So if the enemy is stacking magic pen to counter you, just buy this and zoom straight through their defenses.

Archangel's Staff is great if you get low on mana a lot, because it greatly increases mana, as well as ability power. After building up seven-hundred fifty mana with it, it evolves into Seraph's Embrace, which is basically a beefed up version of Archangel's Staff.

Deathfire Grasp is a great item and is ideal for bursters, that is, if you can remember to use it, which I never can. You can activate it to deal some damage and icrease all incoming magic damage to the target, but it also grants one-hundred twenty ability power. Like I said, all of this is great, but only if you can remember to use it during the fight.

Athene's Unholy Grail, although it's a defensive item, is actually pretty essential to Vel'Koz's build. It grants immense mana regeneration. It also reduces cooldown by twenty percent. So buy it!

Vel'Koz's skill sequence is pretty simple to be honest. All you have to do is max his abilities in order!

Plasma Fission is what you want to max out first. Not only does it slow the enemy when it hits them, but it also goes to the right and left of who it hit! This split is great for poking the enemy all day every day. Although it is kind of hard to land it with the split and all, it is a great ability, and you know what they say! Practice makes perfect! So practice this move versus AI to better yourself against real people.

Void Rift is what you want to max out second. This one is pretty cool, because it'll hit the enemies twice, that is if their stupid enough to stay in spell long enough. The super thing about it, is that it applies two stacks of Organic Destruction! This means that after hitting them with this, you only need to hit them one more time to pop the true damage from Organic Destruction. This ability is also great because it has no cast time, meaning that you can cast while moving, providing some pretty good kiting potental.

Tectonic Disruption is what you want to max out fourth. This is how you hold the enemy in place while you empty your abilities on their butts. This ability will knock up all enemies inside the chosen place, allowing you do DESTROY THEM! Also, if you're close enough to the blast area, then the enimies will also be knocked backwards as well, providing a safe escape if needed.

Life Form Disintegration Ray is what you want to max out third. This, my good friend, will, DESTROY EVERYTHING IN YOUR PATH! That's actually a pretty good description of what the ability does. It fires a beam that will follow your mouse and will damage everything in a line, and it does in fact not stop on the first enemy it hits, meaning you can line 'em up and shoot 'em down. The mouse follow though is very slow so be careful not to begin this while the enemy is close enough to evade it. This ability is also channeled, meaning that a well timed interrupt will stop the ult, pretty much wasting the ult, so be careful on your enemies cooldowns, and if they have interrupts. By the way in case you didn't know, interrupts are spells that stun or knock up or something of that nature.

Barrier is probably one of the better summoner spells that Vel'Koz should use. Vel'Koz is a relatively fragile champion, so Barrier is good for getaways, which you will probably have to do a lot.

Flash is the second one you should take, as well as Barrier, for the getaway potential. I don't know if you've ever done this, but for me, flashing over a wall in the jungle with just a few health left, narrowly escaping an enemy idiot and destroying all their hopes and dreams, but that feeling is MAGICAL! So I just love this one and it's great.

Ghost is a substitute for Flash if you're too low of a level for it. If you are a high enough level for Flash though, than you should probably get it, because Flash moves you immediately, whereas Ghost is slower, and if the enemy is close enough, they can still finish you off, so that's why Flash is better.

Ignite has good potential for finishing off enemies, however, this isn't really needed on Vel'Koz because all of his skillshots have good range anyways, so you can use your abilities instead of this. If you spam your abilities a lot however, this will be useful, because while all of your abilities are on cooldown, they'll be making a clean getaway while you can't do anything about it.

If you're choosing spells other than these, than you're probably doing something wrong.

This is how you actually kill them, using your abilities.

Plasma Fission
Initiate the battle with a well aimed Plasma Fission to slow the enemy.

Tectonic Disruption
While the enemy is slowed, it allows for a much easier chance to land Tectonic Disruption, knocking them into the air, and destroying any hopes for escape.

Void Rift
While the enemy is in the air, empty both of your Void Rift on their butts, which will hopefully, if done correctly, activate two Organic Destruction dealing true damage.

Life Form Disintegration Ray
If the enemy is still alive that is, spray 'em down with Life Form Disintegration Ray and any other champions in your radius of death.

Now, if the enemy isn't dead yet, than you're doing something wrong, or you're up against a well farmed Sion with about a million health points. Enjoy all of the death and destruction!

Bad Match-ups

Veigar
Veigar is probably the worst match-up for Vel'Koz, or any other champion who builds ability power. This is because Veigar ult does a ton of damage, as well as dealing eighty percent of the targets ability power in damage. Which, when you have as much ability power as you're gonna have, which is around five-hundred, Veigar can literally kill you win one hit from full health. So when the other team has a Veigar, just stay away. Very, very, very far away.

Ryze
Ryze is also pretty good against Vel'Koz. He as well as you, is a nuker. The problem is, that he can empty all of his abilities faster than you can. That means that you should only initiate on him when you have more health than him, giving a much more probable chance for survival, and a kill for you. So just don't be stupid when against a Ryze because he might kill you.

Vel'Koz isn't the greatest at teamfights, because he's mainly focused on one versus one battles. When you are in a teamfight though, you're gonna want to stay in the very back casting your spells from back there. If you do however end up in the middle of a teamfight, use Tectonic Destrucion to knock everyone up, and get your but out of there. Because if you stay in there for more than a second, you will die, and very fast at that.